As will be apparent from the references discussed below, it is already known to provide a rotary heart pump which comprises a piston whose path is that of a trochoid with a ratio of 1:2 and which cooperates with a single-lobe chamber to displace fluid from an inlet to an outlet, the piston being driven by an eccentric and having two lobes or corners which are juxtaposed with the surface of the chamber.
Since the outer dimensions of a pump for blood and like sensitive liquids, especially when it is to be used in or as an artificial heart, must be comparatively small, this rotary pump principle which utilizes a minimum space is especially effective.
The pump of the invention is thus intended for use wherever the displacement of blood is desirable, i.e. in clinical situations, as well as for direct implantation in patients and in animals.
It will be appreciated that heart pumps to date have usually concentrated upon a different principle. They have, for the most part, been pulsatile and have utilized membranes or pistons with the force transfer between a pressure plate and the membrane being effected hydraulically and the mechanical movement of the pressure plate being accomplished by an electromechanical, pneumatic or like drive.
The pressure plate can, for example, be operated by an electromagnetic solenoid or the membrane can be actuated directly or indirectly by compressed air or another powering fluid.
These systems have various disadvantages, prime among them being the need to dispose the power source externally of the body because of the size of the power source which must be used. Another disadvantage is the low displacement capability of the pump.
In German patent document No. DE-OS 28 19 851 (corresponding to French Pat. No. 2,389,382 and U.S. Pat. No. 4,296,500), a rotary blood pump is described which is in the form of a trochoid rotary piston pump operating analogously to the rotary pump machines described in Einteilung der Rotations-Kolbenmaschinen--Bauformblatt 16, which describes a trochoid rotary piston pump with a 2:3 or a 1:2 ratio utilizing contact seals between the piston and the chamber wall.
When the pump of these patents is used in a rotational heart application, the electric motor is disposed outside the pump housing and it is clear that a low-speed drive is required. This is understandable because this machine is capable of doing considerable damage to the blood cells, at least in part because of shear which develops at the contact seals at any speed, but most particularly if attempts are made to operate this pump at high speed.
Reference may be had as well to the publication entitled Pulsatile Flow Blow Pump Based on the Principle of the Wankel Engine, von N. Verbiski et al, Journal of Thoracic and Cardiovascular Surgery, vol. 57, 5, May 1963, pages 753-756 in which a 2:3 ratio Wankel machine is described for similar purposes (see Einteilung der Rotations-Kolbenmaschinen, Bauformblatt 18).
All of these rotary machines have the negative characteristic when they are used as blood pumps, that at least a stationary sealing zone of the housing contacts a rotary sealing zone on the flank of the piston so that shear effects and other stresses are applied to the blood cells and at least the red blood corpuscles of the blood are mechanically broken up or damaged, thereby releasing hemoglobin and provoking hemolysis which is at the very least detrimental to a patient.
This is especially the case when the rotary pump must be operated at 200 revolutions per minute or more.